The present invention relates to problems in mixing together the fluids from two tanks, particularly corresponding tanks in two neighboring photographic developing apparatuses. In the type of mixing in question, fluid is withdrawn from plural tanks through respective outflow conduits and pumped through a common mixing conduit which then branches off into plural inflow conduits leading back into the respective tanks.
In large photographic film processing laboratories, it is common that more than one film-developing or printing machine be present and operate simultaneously. When such laboratory has a plurality of simultaneously operating film-developing machines, it is ordinarily desired that the processing fluid in corresponding processing-fluid tanks of the plural machines have exactly identical characteristics, e.g., concentration, temperature, and so forth, in order that the quality and character of the film-development performed by the plural machines be maintained substantially indistinguishable.
With this object in mind, it is known to operate the plural developing machines in an interconnected or in-tandem manner. Corresponding processing-fluid tanks of the plural machines are interconnected, i.e., the developer-fluid tanks of all the machines, the fixer-fluid tanks of all the machines, the bleaching-fluid tanks of all the machines, and so forth. For example, developer fluid is withdrawn from all the developer-fluid tanks via respective outflow conduits; the withdrawn developer fluid is then passed through a common mixing conduit, so that the developer fluid from the various developer-fluid tanks will become intermixed; and the thusly intermixed developer fluid is then branched off via respective inflow conduits and fed back to the individual developer-fluid tanks.
A problem arises when the plural developing machines are of different design and/or located at different elevations, such that the upper level of the fluid in one tank of one developing machine differs from the upper level of the fluid in the corresponding tank or one or more of the other developing machines. This situation may exist, for example, when the plural developing machines are of the same basic operation, but one is of larger dimensions than the others, its tanks for that reason likewise being larger than the corresponding tanks in the other machines and therefore the upper level of fluid in such tanks being higher than in the corresponding tanks of the other developing machines. Alternatively, the plural developing machines may be of similar dimensions, but their mounting structures or housings may hold the tanks at non-identical heights in different ones of the machines. The problem in question can be most especially serious when the plural developing machines are not located at an identical floor height, e.g., because of floor-space layouts in the laboratory.
When these situations are encountered, the resulting hydrostatic pressure differences as among corresponding tanks in the plural machines may make it impossible or difficult to maintain the upper level of fluid in each of the plural corresponding tanks at the proper respective elevation, i.e., if the corresponding tanks are to be interconnected in the manner and for the purpose explained above.